The present invention relates in general to dug wells.
Traditionally, dug wells for domestic use have been constructed with large-diameter (36-inch) concrete “tiles” stacked in a 20 to 30 foot deep vertical hole in the ground that intersects the water table at some depth (Commonwealth of Massachussetts 2008; Maine Geological Survey 2012). This type of well is problematic for several reasons.
First, the water table can fluctuate by several feet annually. This can reduce the available water by more than 30 percent, or more in dry periods, potentially resulting in several days without adequate water supply. Second, the water enters the well from the bottom through an open-bottom tile placed on crushed stone or directly on native materials, limiting the flux face (the opening through which water enters the well). If the well is located in geologic materials with low hydraulic conductivity, the well will be low yield and may not provide adequate supply. Further, traditional dug wells are round (non-directional), which at first glance seems desirable because water can flow into the well from any direction. However, groundwater typically comes into the well primarily from the area upgradient of the hole. Because the geologic material (sediment) often is of low permeability, these wells are limited by the available inflow area (flux face) and by their relatively low storage capacity. Third, the traditional dug well is susceptible to contamination from bacteria. The combination of stacking large diameter well tiles made of concrete, and a typically inadequate concrete seal at the well cap on the top of the well, often results in unsanitary seals, allowing insects, rodents, and runoff carrying bacteria to enter the well.
Also, anoxic and alkaline aquifers in some parts of the United States commonly contain high concentrations of arsenic (Ayotte et al. 2003; Ayotte et al. 1999; Ayotte et al. 2006; Flanagan et al. 2012; Montgomery et al. 2003; Nuckols et al. 2011; Smedley and Kinniburgh 2005; Welch and Stollenwerk 2003). For example, high concentrations of arsenic are known to affect 20 to 30 percent of private drilled wells in Maine and New Hampshire, as well as other parts of the United States. It is estimated that more than 100,000 people use private drilled wells in eastern New England that have unsafe levels of arsenic (Ayotte et al. 2003). As a result, many state and local agencies have been looking for ways to mitigate arsenic problems in private domestic wells.
Thus, traditional dug wells commonly have poor yield, are subject to drought failure, and often contain bacteria or other contaminants. An improved well design is needed to provide safe drinking water in larger quantities.